1. Field of the Invention
The present invention relates to an image recording and erasing method for clearly recording images and erasing the same repeatedly for an extended period of time by use of a reversible thermosensitive recording medium which is capable of reversibly changing the transparency and/or color thereof depending upon the temperature thereof.
2. Discussion of Background
Recently attention has been paid to a reversible thermosensitive recording medium which is capable of recording images temporarily therein and erasing recorded images therefrom when such images become unnecessary, and which is also capable of performing such image recording and erasing operations repeatedly.
Representative examples of such a reversible thermosensitive recording medium are disclosed, for instance, in Japanese Laid-Open Patent Applications 54-119377 and 55-154198, in which an organic low-molecular-weight material such as a higher fatty acid is dispersed in a matrix resin such as a vinyl chloride-vinyl acetate copolymer.
However, when images are formed in such a conventional reversible thermosensitive recording medium and erased therefrom repeatedly many times by the application of heat thereto, in particular, by using a thermal head, the surface of the reversible thermo-sensitive recording medium is scratched because the surface is fractioned while heat is applied thereto, and eventually it becomes impossible to form images uniformly on the recording medium.
Furthermore, for instance, when a heat application system, by use of a thermal head, which applies both head and pressure to the recording medium, is employed, particles of the organic low-molecular-weight material aggregate as the repeated number of recording operations is increased. As a result, the contrast of images, that is, the degree of white opaqueness thereof, is lowered.
For reducing such deterioration of the reversible thermosensitive recording medium, a method of heating a reversible thermosensitive recording layer by use of a non-contact heat application means has been proposed and known. According to this method, even if the reversible thermosensitive recording layer is softened by the application of heat thereto, no pressure is applied thereto, so that the deterioration of the recording medium can be reduced. For example, Japanese Laid-Open Patent Application 57-82088 proposes a method recording images by the application of a laser beam to reversible thermosensitive recording medium which comprises (a) a reversible thermosensitive recording layer which contains carbon black or (b) a carbon-black containing layer which is provided in close vicinity to a reversible thermosensitive recording layer. According to this proposed method, non-contact recording can be performed, but obtained images are grayish in entirety thereof and the image contrast thereof is considerably low either when carbon black is contained in the reversible thermosensitive recording layer or when the carbon-back containing layer is provided in close vicinity to the reversible thermosensitive recording layer as mentioned above.
Furthermore, Japanese Laid-Open Patent Application 64-14077 proposes the same method as mentioned above except that the carbon black is replaced by an infrared absorbing dye. According to this proposed method, the image contrast is slightly improved in comparison with the case where carbon black is employed, but the infrared absorbing dye absorbs visible light, so that the obtained image contrast is still low and insufficient for use practice.